Howdy from the Houston area!
I've seen western style leather vests worked into casual kilt outfits fairly often down here, and western belts and buckles as well, but not as often. I didn't think that look was too far out, so I'd say why not give them a try. On the other hand, I've seen some kilt and cowboy boot combos as well, but I aways thought that looked more like a attempt at humor than a legit fashion choice.